Mineral oil composition



Patented June 6, 1944 MINERAL OIL COMPOSITION Everett W. Fuller,Woodbury,

N. 1., assignor to Snoo y-Vacuum Oil Company, Incorporated,

New York, N. Y.,

a corporation of New York No Drawing. Application November 26, 1941,

Serial No. 420,465

4 Claims. (01. 252-45) This invention relates in a general way to thestabilization of viscous mineral oil fractions against the deleteriouseffects of oxidation or deterioration with use through the agency ofoxidation inhibitors. More specifically, the present invention isconcerned with the improvement of viscous mineral oil fractions by useof novel compounds, or a novel class of compounds, which when admixedwith a viscous mineral oil in minor proportions will prevent or delayundesirable changes taking place in the oil. The invention isparticularly concerned with the productionof mineral oil compositionsadapted for use in turbines and transformers.

As is well known to those familiar with the art, substantially all thevarious fractions obtained from mineral oils and refined for theirvarious uses are susceptible to oxidation. The susceptibility of an oilfraction to oxidation and the manner in which oxidation manifests itselfwithin the oil varies with the type and degree of refinement to whichthe oil has been subjected and with the conditions under which it isused or tested. Thus, the products formed in an oil fraction as a resultof oxidation and the degree to which they are formed depends upon theextent to which the various unstable constituents or'constituents whichmay act as oxidation catalysts have been removed by refining operations,and also upon the conditions of use.

A highly refined viscous oil, for example, which is one that has beenrefined by treatment with fuming sulfuric acid or other means orcombinations such as AlCls, solvents and acids (or with large quantitiesof concentrated sulfuric acid),- tends to form relatively large amountsof acidic constitutcnts when subjected to oxidizing conditions. Thepresence of catalytic materials such as copper does not appear to affectappreciably the oxidation of highly refined oils, and such oils are lessprone to the formation of colored bodies or of insoluble sludge than aremodrate v refined oils or solvent refined oils. The

formation of acidic bodies. however, is highly undesirable for m stapplications of these oils. For example, when used as an insulating orcooling oil in electrical equipment such as transformers or capacitorsan increase in acidic bodies tends to lower the dielectric strength ofthe oil and has ot er harmful effects which are undes able. The acidsare corrosive to metals and thus reduce the useful life of the oils aslubricants or for other purposes in which they come in contact withmetals,and the acidic materials 55 are also injurious in textilelubricants and in spray oils.

Moderately refined oils, that is, oils that have been refined bytreatment with only moderate amounts of sulfuric acid, or other refiningagents, will form substantial quantities of insoluble sludge whenused inturbines and electrical transformers. Such sludge formation clogs thepipes and vents in the oil circulation system of a turbine and thecooling ducts of a transformer. By forming films on the insulation, itreduces the heat transfer in electrical transformers and in addition itsubstantially reduces the dielectric properties of the oil. The changestaking place in these oils are appreciably accelerated by the presenceof metal catalysts such as copper. Not only do they form considerableamounts of insoluble sludge, but they undergo material color formationsand form sufiiclent acid to cause some reduction in the dielectricstrength of these oils when in the presence of metal catalysts.

Solvent refined oils in general, which have been prepared by treatmentwith selective solvents, such as chlorex, phenol, furfurai, etc.,resemble the moderately refined acid-treated oils in that their oxdation is accelerated by the presence of metals such as copper andfurther in that it is attended by substantial color depreciation andsludge formation. Acid formation is usually greater than in the case ofmoderately acidrefined oils, but considerably less than with highlyrefined oils. Both sludge and acid formation lower their value for manypurposes, such as electric insulation, lubrication, etc. Also,solvent-refined oils have found extensive use as lubricants for internalcombustion engines because of their high viscosity index, but under theconditions of use encountered in crank cases such oils developconstituents which'arecorrosive toward certain metal bearings such asthe cadmium-silver bearings, etc., which are sometimes used.

The high cost, as a result of high treating losses and the largequantities of refining agents used, of the highly refined oils has beenresponsible for the investigation of means by which oil fractionsmoderately refined and. solvent refined to meet turbine and transformerspecifications might be further enhanced by the addition of acharacterizing agent thereto. 'Such an agent would act as a negativecatalyst or inhibitor to retard the formation of sludge, acid and colorbodies under the aforesaid conditions of use. As a result of theseinvestigations, numerous compounds havebeen proposed for use disulfidein mineral oils 1 tion upon said fr'actions ing suchan inhibitor posedto light.

blends containing the for use at normal temperatures may show a pre-'cipitate of the inhibitor if it is subjected to subnormal temperatures.Alsor solutions of aniline are only moderately stable to light and onprolonged exposure to light they tend to cloud and later to show anincreasingly heavy precipitate.

As aforesaid, one object of this invention is the production of improvedbilized against the deleterious effects of oxidaby the addition theretoof a compound which possesses outstanding qualities-as a negativecatalyst or inhibitor. A fur- ,ther object of this invention is theproduction of an inhibited mineral oil composition comprisand amoderately refined oil or solvent refined form considerable sludge, andsome acid and color bodies, under the conditions of use encountered inturbines and transformers.

The present invention is predicated upon the' mineral oilfractionsstasodium sulphate, and

aasdvso A' solution of sodium disulflde was formed by of NasSMizO and0.7 gram of sulphur in 50 c. c. of ethyl alcohol. This solution wasadded to 6.0 grams of z-nitro-i-p-tertiary butyl chlor benzene dissolvedin 50 c. c. of ethyl alcohol. The mixture was refluxed for one hour,then cooled and poured into 500 c. c. of water. The viscous oil wasextracted with ethyl ether, washed with water, dried over anhydrous thesolvent distilled off. left4,4'-dletertiarybutyl-2,2'-dinitro-dldissolving 5.3 grams This . phenyldisulphide, which was reduced to the corresponding amino compound. To amixture of 9.8 grams of iron powder and 65 c. c. of water containing 0.6c. c. of glacial acetic acid were added 4.0 grams f the dinitrocompound, and the resuiting mixture warmed to 80-90 C. for 10 hours.

oil that normally tends to v discovery that alhlated diamino diphenyldlsulfides' represented by the general formula 1: a 11' a H\ n n a n a aa R wherein, R and R consisting of hydrogen and alkyl radicals, at leastone B and at least one Rf always being an alnl radical, arehighlyeffective in small amounts in mineral oilsin accomplishing the foregoingresults.

The carbon-alkylated (C-alkylated) diamino diphenyl disulfldes, of thetype contemplated herein, are inexpensive to prepare and are readilysoluble in viscous mineral oil fractions. Their increased solubilitymakes them superior to aniline disulfide. In addition to increasedsolubility, the alkylated compounds contemplated herein produce 011blends which are surprisingly superior to aniline disulfide in As afurther improvement over oil blends containing aniline disulfide, theoil C-alkylated compounds contemplated herein are stable against thedevelopment of a cloud in the oil at subnormal temperatures. Theformation of a cloud depends upon, the concentration used, the coolingtemperature and the cooling cycle. Themuch greater oil solubility ofthese new compounds makes them much less liable to cloud on cooling.

Alkyl diamino diphenyl disulfldes contemplated herein arereadilymrepared by any of the standard methods described in theliterature.- 'Ihus.

are selected from the group color stability when ex- 1 The reactionmixture was then extracted with benzene and the benzene extract washedwith water, dried, and the solvent removed. by distillation. The productwas further purified by dissolving it in dilute acid, filtering, andrepreclpi- .tating by adding an alkali. The4.4'-ditertiarybutyl-2,2'-diamino diphenyl disulphide thus obtained onanalysis showed:

llouud Theory Per cent sulphur l 11.02 11.11 Per cent nitrogen 7. 82 7.71

The following test examples illustrate the effectiveness of the class ofcompounds and certain specific members within the class contemplatedherein as inhibitors for mineral oil fractlons.

Tss'r No.1

Highly refined oils The oil used in this test was one suitable for usein transformers and had been prepared by treating a Coastal distillatewith 40 pounds of 98% sulphuric acid and 180 pounds of 103% oleum perbarrel, followed by washing and clay percolation. It had a specificgravity of 0.871, a flash point of 310 F., and a Saybolt Universalviscosity of 69 secs. at 100 F. This type of oil tends to form acidicproducts on oxidation. It "was tested by heating samples to 120 C. andbubbling oxygen therethrough for .a period of 70 hours. The acids thusformed were removed by titrating with alcoholic potassium hydroxide, theacidity being indicated by the so-called neutralization number (N. N),which is the amount in milligrams of KOH required to neutralize theacids formed in one gram of the oil. The results of this test on the oiland oil blend are given in Table I below.

. Table I I Compound added m N. N.

None 25.0 4;4'-di-tertiarybutyl-2,2-diamino-diphenyl disulfide 0.10 0.01

, Tss'r No. II I Moderately refined oils refined by treatment with '70pounds of 98% sulphur c acid per barrel, neutralized, washed, and

percolated through clay. It had a specific gravity of 0.879, a flashpoint of 383 F. and a Saybolt Universal viscosity of 152 secs. at 100 F.This is an oil suitable for use in turbines, and the test used involvedheating 25 c. c. samples of the oil and oil blends to a temperature of200 F. with liters of air per hour passing therethrough. During the testthe oil was maintained in contact with copper and iron by adding 24inches of 18 gauge copper wire and one gram of iron granules to eachsample. Also, during the test 2 c. c. of distilled water were added eachday, and the samples were tested for acidity or neutralization number,color and sludge formation at varying periods of time. The results ofthese tests with this 011 blends of the. same oil containingrepresentative compounds of the type contemplated herein are set forthin Table II below, from which it will be observe that all of thesecompounds show an apprecia le eflect in inhibiting the deterioration ofthis type of oil.

Solvent refined oil The oil usedinthis testwas adistillatefrom a RodessaCrude which has been refined by solvent extraction with .iurfural,dewaxed and illtered. The finished oil had a specific gravity of 0.856,a flash point of 420 F., and a Saybolt Universal viscosity of 151 secs.at 100 F. It was tested by the same procedure followed in .Test No. II,and the results obtained are set forth in Table III below.

Table III f .Pc' 1 Low. Sludge cent E." N'N' color mg./25c.c.

or 0.91 19 3a 165 are 320 251 4,4"di-tertisrybntyl- 2,2'-diamino lmnyl167 a1 1 1 disulfi e P 0.10 ass as 1 a 601 51s a 57 4,4- diamyl-2,2'diamifio dlphenyldisulflde-- 0.10 :2: fig; i}

It will be observed from the foregoing tabulated results that thealkylated diamino diphenyl disulfides when used in small amounts inmineral oil fractions potentially susceptible to the formation ofsludge, acid, and color bodies, are highly efiectlve inhibitors of saidformation.

As' aforesaid. one important and surprising advantage of the C-alkylateddiamino diphenyl disuliides over the unalkylated compound (diaminodiphenyl disulfide or aniline disulfide) resides in the greater lightstability of oils containing the former compounds of the presentapplication, over oils containing the aniline dissulfide of the priorart. This is demonstrated by the fact that on exposure to ordinary roomlight an oil containing 0.1% of diamino diphenyl disulfide became cloudywithin 14 days and showed an appreciable precipitate by 122 days;whereas, the same oil containing 0.1% of a C-alkylated diamino diphenyldisulfide (4,4'-tertiarybutyl- 2,2'-diamino diphenyl disulfide) was onlyslightly cloudy after 48 days and showed only a very slight trace of aprecipitate in 122 days.

It is to be understood that the terms highly refined," moderatelyrefined-and solvent refined as used herein have reference to oilscorresponding substantially in their manner of deterioration andinhibitor response to the examples given and are not necessarilyrestricted to oils obtained by particular refining operations. As hasbeen previously pointed out, the final characteristics in an oilfraction are effected by the crude from which the oil is obtained aswell as the refining treatment, and by selection of the crude stock, anoil of the highly refined" type may be obtained by a treatment which onanother crude stock would yield an oil having the characteristics of amoderately refined oil.

The amount of the inhibitor used may be varied, depending upon the oilfraction and use to which it is put, from about 0.01% to about 1.0%. Ingeneral, the amount satisfactory for substantial inhibition will be ofthe order of from about 0.05% to about 0.5%.

I claim:

1. An improved mineral oil composition comprising a viscous mineral oilfraction and in admixture therewith a minorproportion of4,-i'-ditertiarybutyl-2,2'-diamino diphenyl disulfide in an amountsufiicient to inhibit the deleterious effects of oxidation upon the oil.

2. A mineral oil composition of the type adapted for use in turbines andtransformers comm ing a moderately refined mineral oil potentiallysusceptible to the formation of sludge under the conditions of usenormally encountered in turbines and transformers, and a minorproportion of 4,4'-di-tertiarybutyl-2,2'-diamino diphenyl disulfide inan amount sufilcient to resist the formation of said sludge under saidconditions of use.

3. An improved mineral oil composition comprising a viscous mineral oilfraction and in admixture therewith a minor proportion, sufilcient toinhibit the deleterious effects of oxidation upon the oil, of a compoundselected from the group consisting of 4,4'-di-tertiarybutyl-2,2'-diaminodiphenyl disulfide and 4,4'-diamyl-2,2'-diamino diphenyl disulflde.

4. A mineral oil composition of the type adapted for use in turbines andtransformers comprising a moderately refined mineral oil potentiallysusceptible to the formation of sludge under the conditions of usenormally encountered in turbines and transformers, and a minorproportion, sufiicient to resist the formation of said sludge under saidconditions of use, of a compound selected from the group consisting of4,4'-di-tertiarybutyl-2,2-diamino diphenyl disulfide and4,4'-diamyl-2,2'-diamino diphenyl disulnde.

EVERE'IT W. FULLER.

